SOUTH PORTLAND – Carbon monoxide poisoning is being blamed for the hospitalization of five people who lived in a duplex in South Portland.

According to the Fire Department, emergency crews were called after a relative found a woman and her 10- or 11-year-old son passed out in their Hill Street apartment Sunday night. Three other people who were in the second unit complained of headaches.

Fire Department spokesman Rob Couture said firefighters detected high levels of carbon monoxide, and that a propane heater may be to blame.

All five people, whose names haven’t been released, were taken to Maine Medical Center. Couture said the mother and son were expected to taken to a Boston hospital for treatment.